Active implantable devices generally include a housing commonly referred to as the generator. The generator is typically electrically and mechanically connected to one or more intracorporeal “leads.” These intracorporeal leads are electrodes which are intended contact the bodily tissues (e.g., myocardium tissue, nerve tissue, muscle tissue, etc.) to which electrical stimulation pulses are applied and/or from which an electrical signal is collected.
Standardized connection systems exist to ensure interchangeability of the leads and generators produced by different manufacturers. For example, “IS-1” and “IS-4” standards define a number of dimensional and electrical characteristics relating to pacing or resynchronization pulse delivery leads. For defibrillation leads, wherein the electrical stresses are most severe in view of the high energy to be channeled from the generator to the lead, the “DF-1” and “DF-4” standards define dimensional and electrical characteristics of the connection system.
The present invention more particularly relates to a multipolar electrical connection plug for a lead for an active implantable medical device. A multipolar electrical connection plug is a single-body lead including both stimulation and shock electrodes. The complexity of these leads, which is high due to specific constraints in terms of power related to one or the other uses (i.e., stimulation or shock), is further enhanced by the development of multisite devices and intracardiac sensors such as endocardial acceleration (EA) sensors.
Some leads have a single plug and a plurality of electrical contacts. The plurality of electrical contacts simultaneously connect to various terminals of the generator (e.g. for various energy levels). For example, each of the plurality of electrical contacts may connect to a different generator terminal for the collection of depolarization signals, for the application of pacing pulses, for the delivery of a defibrillation shock energy, or for the transmission of signals collected by a sensor. An advantage of leads having a single plug is that single-plug leads can be subject to single standard. In this context, a single “multipolar” and “isodiameter” connector (e.g., having multiple contacts and a smooth cylindrical shape) to be inserted in a counterpart cylindrical cavity of the connector head of the generator is in compliance with the IS-4/DF-4 standard (ISO 27186-2010).
European Patent Application No. 1641084 A1 and its U.S. counterpart U.S. Patent Application Publication No. 2006/0068645 describe an example of such a four-pole connection plug. Connection plugs of those applications are of the isodiameter type having an axial electrical contact pin at one end. Connection plugs of those applications also have three annular electrical contact areas on the body of the plug. The annular electrical contact areas are made by consecutive cylindrical rings and are alternately separated by intercalary insulating cylindrical areas. The insulating cylindrical areas electrically isolate the electrical contact areas from one another. Accordingly, it is possible to simultaneously perform all the necessary electrical connections between the generator and the lead pins in a single movement by inserting the connection plug into the cavity of the connector head of the generator.
However, the realization of such a connection plug raises many manufacturing problems and challenges. ISO standards constrain the outer diameter to merely 3.2 mm (e.g., according to ISO 27186), thereby limiting design possibilities. The impact of compliance with such tight dimensional tolerances in an industrial manufacturing process can be significant in terms of time and cost.
A further difficulty arises with respect to “coaxial configuration” leads. Coaxial configuration leads include a mobile central conductor housed in an axial lumen of the lead body and a plurality of other conductors extending from a periphery of the lead body. The axial contact pin is connected to the central conductor. The pin-conductor assembly has a rotational degree of freedom relative to the outer body of the plug and relative to the lead body.
Coaxial configuration leads are mainly used to allow an anchoring screw deployment mechanism (e.g., located at a distal end of the lead) to be driven by manipulation of the proximal end of the lead (e.g., wherein the plug is). For example, a surgeon may hold the proximal end of the lead body with its plug connection with one hand and rotate the pin extending from the plug with the other hand. The torque applied to the pin is transmitted via the inner conductor to the deployment and driving mechanism of the anchoring screw, which allows control of the penetration of the latter into the heart wall. Such a pin-driven lead structure is described, for example, in U.S. Pat. No. 7,241,180 B1 and U.S. Patent Application Publication No. 2010/0211144 A1.
The presence of a movable element in the plug of coaxial configuration leads causes additional difficulties in the design and manufacturing thereof. One difficulty in the design of coaxial configuration leads is attributable to the need to maintain specific dimensional tolerances (e.g., specified by ISO standards) while achieving a minimum functional space necessary for free rotation of the axial pin. Another difficulty is attributable to sealing requirements. In some cases it is advantageous to provide sealing between the external environment and the internal regions of the plug and of the lead body (e.g., including the central lumen which receives the mobile axial conductor). Such sealing functions to prevent the penetration of body fluids between the mobile parts and in the inner areas of the plug and of the lead body. Sealing can be important in the case of a lead with defibrillation electrodes, given the important electrical energy and the high voltage passing through the plug during the application of the defibrillation shock. The structure of such a plug and the method of assembly of the mobile axial pin are challenging and difficult aspects of both the plug design and the implementation of the manufacturing method.
U.S. Patent Application Publication No. 2010/0211144 A1 discloses a pin mounting assembly having two concentric members. The disclosed assembly has a ring-shaped part mounted around the shaft of the pin (e.g., acting as a bearing if the pin is mobile in rotation) and a circumferential collar surrounding the ring around its periphery. The circumferential collar acts as a coupler with the plug body and is encapsulated or screwed during manufacturing. This configuration allows a rotational degree of freedom between the pin and the plug body if necessary. However, the pin mounting assembly disclosed in Publication No. 2010/0211144 leads to a relatively complex and expensive manufacturing process, requiring the production of parts with very tight tolerances in order to meet the imposed dimensional constraints. More importantly, the disclosed configuration fails to provide a satisfactory solution to the issue of very narrow tolerances despite the presence of mobile parts (e.g., the pin possibly being handled without axial or radial clearance with respect to the lead body). Additionally, the disclosed configuration fails to adequately provide absolute tightness of the internal regions of the plug and of the lead body with respect to the external environment.